In recent years, as one of the methods for synthesizing liquid fuels from natural gas, the GTL (Gas To Liquids: liquid fuel synthesis) technique has been developed. In the GTL technique, natural gas is reformed to produce a synthesis gas containing hydrogen gas (H2) and carbon monoxide gas (CO) as main components, hydrocarbons are synthesized by the Fischer-Tropsch synthesis reaction (hereinafter referred to as “FT synthesis reaction”) with a catalyst using the synthesis gas as a source gas, and the hydrocarbons are hydrogenated and fractionated to prepare liquid fuel products, such as naphtha (crude gasoline), kerosene, gas oil, and wax.
Conventionally, as a hydrocarbon synthesis reaction apparatus which synthesizes hydrocarbons by the FT synthesis reaction, a configuration including a reactor which stores catalyst slurry having solid catalyst particles suspended in a liquid, and a synthesis gas supply line through which a synthesis gas supplied from a synthesis gas supply device which supplies the synthesis gas to the reactor is known. According to this hydrocarbon synthesis reaction apparatus, hydrocarbons can be synthesized by the FT synthesis reaction by contacting the synthesis gas and the catalyst slurry in the reactor.
In the above hydrocarbon synthesis reaction apparatus, the pressure in the reactor is higher compared to normal pressure, and the temperature of the reactor is higher compared to normal temperature in the FT synthesis reaction, so that the FT synthesis reaction is smoothly performed in the reactor.
In this type of hydrocarbon synthesis reaction apparatus, there is a possibility that supply of the synthesis gas to the synthesis gas supply line from the synthesis gas supply device may be stopped due to, for example, unexpected external factors (earthquake, power outage, or the like). In this case, the problems shown below may occur as the fluidization state of the catalyst slurry in the reactor is deteriorated.
First, as the FT synthesis reaction is continued with the synthesis gas remained in the reactor, the reaction heat released by the exothermic reaction is not efficiently removed because of the deterioration of the fluidization state of the catalyst slurry, a hot spot is temporarily formed in the catalyst slurry, and a part of the catalyst may possibly deteriorate by the excessive temperature rising. In this case, there is a problem in that the yield of the hydrocarbon synthesis by the FT synthesis reaction decreases after resumption of the operation at which the supply of the synthesis gas from the synthesis gas supply device has been resumed, compared to before stoppage of the operation at which supply of the synthesis gas has been stopped.
Moreover, the catalyst particles may be clogged in the synthesis gas supply line. In this case, there is a problem in that the synthesis gas from the synthesis gas supply device is not smoothly supplied to the reactor after operation is resumed, and in the worst case, the synthesis gas is not supplied at all.
Thus, for example, as shown in the following PTL 1, a method of supplying the other gas to the reactor, and securing the fluidization state of the catalyst slurry in the reactor when the supply of the synthesis gas to the reactor has been stopped is suggested.